Method of producing and controlling a space discharge



June 23, 1936. J. H. o. HARRIES 2,045,525

METHOD OF PRODUCING AND CONTROLLING A SPACE DISCHARGE Original Filed Feb. 26, 1952 s Sheets-Sheet 1 W wm June 23, 1936. HARRlEs 2,045,525

METI'iOD OF PRODUCING AND CONTROLLING A SPACE DISCHARGE Original Filed Feb. 26, 1932' 3 Sheets-Sheet 2 I NVENT a *4 M June23, 1936. J. H. 0.. H-ARRIES 2,045,525

A METHOD OF PRODUCING AND CONTROLLING A SPACE DISCHARGE Original Filed Feb. 26, 1932 3 She'ets-Sheet s Fgzi Y Patented June 23, 1936 PATENT. orrlce METHOD OF PRODUCING AND CONTROL LING A SPACE DISCHARGE John Henry Owen Harries, Frinton-on-the-Sea, England Application February 26, 1932, Serial No. 595,339. Renewed March 2'), 1936. In Great Britain March 10, 1931 41 Claims. (Cl. 25027) I i.

This invention relates to the production and control of ionic streams particularly, though not exclusively, to discharge tubes where the current is varied in intensity by some means (for instance by deflecting the stream as in my British Patent No. 328,680) and these variations are employed to energize a'load usually connected in the'anode circuit of the tube. v

In electric discharge vacuum tubes, streams of electrons .the lengths of which are great in proportion to their cross section have the advantage that the capacities between electrodes can be greatly reduced, and the undesirable retrograde movement of secondary electrons from'the anode is prevented. Furthermore, such streams of electrons can, in contradistinction to shorter streams, be deflected to a considerable degree and consequently can be used in tubes which are worked by deflection of the stream of electrons therein, for the purpose; for instance, of multiplying frequencies. (For this purpose, for example, a stream of electrons may be periodically moved by means of an alternating current over a perforated plate acting as the anode, so that a series of current impulses is produced in a closed output circuit connected to this plate.) Hitherto, however, the ratio between the voltage used to produce the space current, and the intensity of the current, in such streams of electrons which are long and small in cross section, has been so high that known apparatus worked by such streams of electrons have been unsuitable for practical use in incandescent cathode tubes and the like. Therefore, previous practice has been confined to the use of tubes with streams of electrons the lengthsof which were comparatively short in proportion to their crosssections, (and which were produced by voltages which were comparatively small in proportion to the intensity of the current), although such tubes exhibited disadvantageously high-capacities between the electrodes a tendency toward the undesirable retrograde movement of secondary electrons, and .the streams therein cannot be deflected to any useful extent.

One object of the present invention is the production of streams of electrons in which the ratio of the voltage to the intensity of the current is small, and the length in proportion to the cross section is great, whereby the disadvantages of the two kinds of streams hereinbefore mentioned are avoided.

Ewamples of apparatus The operation of the invention will now be be used with the tube;

described with reference to the accompanyin drawings, wherein Figure 1 shows a'highly evacuated tube which will operate according to the invention;

Figures 2, 3, 4 and 5 are electrodes in such a 5 tube;

Figures 6, '7, 8 and'9 are forms of characteristic curves obtainable with such a tube;

Figures 10 andf12 represent'circuits which can Figure 11 is a form of curve obtainable with w the-circuit shown in Figure 10; I

Figures '13, 14, 15 and 16 represent further circuits illustrating the combination of electrodes;

Figures 17 and 18 show sections at right angles of a tube suitable foruse as a frequencymultiplier as described in British Patent No. 328,680;

Figures 19, 20, 21, 22, 23 and 24 are electrodes in such a tube;

Figure 25 is a form of curve obtainable with such a tube. I

Similar parts in difierent figures have the same reference marks. l

The word mesh will be meant to include what is meant by a grid or grating when here applied to electrodes having apertures.

In Figure 1 the tube l is highly evacuated. The a cathode 2, Figure 2, which can conveniently consist of a flat pancake spiral, is heated in the usual way so as to emit electrons. A circular hood 3, Figure '3, is arranged. partly to enclose the cathode 2, leaving it open towards an accelerating electrode 4, Figure 4. Separate electrodes which may form a divided anode 5, 5' Figures 1 and 5 are mounted in the tube I in such a manner that thedistance d from the accelerating electrode 4 may be adjusted. The glass rods 6 forming Part of the pinch l at the end of the tube support two brackets 8 which are connected by means of the wires 9 and 9' to the outside of the tube. The anode 5, 5' is supported on two rods Ill connected by glass rods I4 which slide in holes in the brackets 8. Thus the characteristics may be altered for design purposes as aforesaid. The brackets 8 and rods I0 are both of metal and the anode 5, 5' is therefore in electrical connection with the outside of the tube. The distance it may then be adjusted by moving the tube and sliding the anode 5, 5' to a dinerent position. The accelerating electrode 4 con- -sists of a mesh 6, the spacing between the wires of the mesh being indicated by s.

This tube illustrates a simple form of apparatus made in accordance with the present inven- 55 from the cathode 2 to the anode 5, 6'.

tion and its operation will be described with reference to Figures 6, '7, 8 and 9 which are the characteristic curves of the apparatus. In Figure 1 the cathode 2 is assumed to produce a space charge and it is required that a substantial portion of the electrons therein be made to form a stream F gure 6 shows the form of the curve connecting the anode voltage E. and the anode current and the current to the accelerating grid 4. The curve a is that of the accelerating grid current and that marked a is the curve of the anode current. For purposes of explanation it will be assumed that the distance d is about 7 cm., the voltage of the accelerating electrode 4 is about 200, and that the anode voltage is gradually increased from zero upwards as shown in Figure 6. It will be seen that the entire space current goes to the accelerating electrode when the anode voltage is below a certain point. when this point has been reached the anode current rises fairly suddenly to a saturated value, the grid current dropping by a proportional amount. Once this point has been passed the anode current and grid current are saturated and the grid current is only a small portion of the total. The anode voltage at which the anode current becomes saturated will be referred to as the breakdown voltage of the tube. It is indicated by Eb on the graph Figure 6. A typical value of the anode current density after breakdown may be between 10 and 15 m. a. per square cm. of the cross section of the stream when d is '7 cm. Whatever the anode and accelerating grid voltages which are employed the ratio between the accelerating grid and anode currents are substantially constant at all anode voltages over the breakdown value.

In Figure 7 the "breakdown voltage Eb is plotted against the distance d in cm. This will be referred to as the distance curve. It will be seen that Eb rises very rapidly with an increasing value of d (providing certain conditions as regards the electron velocities, etc. are fulfilled) but has a minimum. This point occurs when the anode is fairly close to the accelerating electrode. The rise in Es for smaller values of d is due to secondary radiation from the anode reaching the accelerating electrode. This transfer of secondary radiation is small, and not unduly detrimental, where the rate of change of the distance curve is only slightly negative.

The distance d may be set at this critical value (say 3 cm.) and at this point the breakdown voltage will be so low that it is possible to allow the anode voltage to become much less than the accelerating voltage without its going below the breakdown point and the anode current ceasing to be saturated. This is of particular importance when a load is connected in the anode circuit across which a considerable voltage drop is developed under working conditions. If the tube has a load impedance in the anode circuit, the current through which is to be varied in use, it will be realized that a considerable waste of power will occur if the anode voltage swing under working conditions has to be accommodated entirely above the accelerating voltage. This value of at when Eb is at a minimum will be referred to as the critical anode distance.

In Figure 8 a typical graph between Eb and the anode current Ia for a given value of the distance d and the'accelerating electrode voltage Eacc is shown. It will be seen to drop very rapidly for a certain range of values with a reduction in the anode current. It is also found that the shape of this graph is considerably aifected by the emcacy of the focussing action of the electrodes. e. g. that of the hood 3 in Figure 1. L may be varied without altering Eace by, for instance, varying the heating current to the cathode 2.

In Figure 9 the anode and accelerating grid currents are shown as functions of Ence, with a constant value of d and with E. greater than Eb, i. e. with the anode current in the saturated condition. The graphs are marked as in Figure 6. It should 10 be noted that both are smooth and that the curve of their sum would be similar to that which one would expect to obtain if the accelerating electrode 4 in'Figure 1 were a solid plate and did not pass any of the electrons on to the anode. If, however, the anode voltage falls below the breakdown point the graphs in Figure 9 will tend to cross.

Referring again to Figure 1, the accelerating electrode 4 is spaced by the distance r from the cathode. This distance is set to give the required space current at the voltage of the accelerating electrode to be used. The distance 3 between the wires in the mesh 6 is suitably arranged so that the apertures between the wires are not too small compared with the distance r in order to reduce the amount of current intercepted by the electrode 6. The distances 3 and r are a matter of compromise and are best determined by experiment in any given case. The wires forming the mesh 6 should be as thin as possible, and, when the tube is working above the breakdown point in accordance with the present invention, the dissipation of anode current to these wires will not be excessive. In Figure 1, r may be about 2 mm. and 3 about 1 mm.

In a typical tube embodying the invention, the hood 3 will be of approximately one centimeter diameter with the cathode of slightly smaller area than the cross-sectional area of the hood and the accelerating electrode 4 will be approximately two centimeters square with 20 wires spaced apart at a distance of one millimeter and the anode 5 will be approximately three centimeters in diameter. The potential Eacc applied to the accelerating electrode 4 will be from 200 to 250 volts and the anode current will be 10 to 20 milli-amperes. In such a tube, the critical distance do will be from two to three centimeters.

It will be realized by those skilled in the art that, as is usual in electron discharge tubes, the best design for an actual tube for given purpose is best found by experiment, and that the exact form of the characteristics will vary considerably with the exact electrode assemblies used, although they will have characteristics broadly as shown. For this reason the design of a tube for a given purpose is best approached by means of a series of tests with movable electrode arrangements such as that shown in Figure 1. By this means the best compromise between the various quantities and the most satisfactory type of electrode to use will be easily ascertained. The value of various quantities quoted are thus only given for purposes of explanation and it is u'hderstood that they may be varied widely without departing from the scope of the invention. A trial tube can be constructed with movable electrodes to determine the best electrode assembly.

It will .be seen that an essential characteristic of the tube illustrated in Figure 1 is that the differential impedance of the anode circuit is high. This is usually desirable. By interconmeeting the anode 5 and, in this case, the accelerating grid 4 it is possible to reduce the impedance if required, as follows.

In the following figures a load is represented by a numeral l5.

Examples of transferred potentials In Figure 10 the tube I is shown diagrammatically with the cathode 2, accelerating electrode 4 and anode 5 represented therein. The distance d between the accelerating electrode 4 and the anode 5, 5' is assumed to be large. The battery II is connected to the anode 5, 5' in the usual manner to produce the anode current. Assuming that the tube is being employed as a relay or in other ways requiring that variations in the anode current are to operate a load impedance, this latter may be connected at [5 between the battery It and anode 5, 5, For instance, the anode 5 may be acting as the target electrode 1 in Figure 2 of my above mentioned British patent. The resistance R is connected between the anode 5, 5' and accelerating electrode 4. In accordance with the present invention the resistance R is of such a value that a considerable portion of the anode voltage is transferred to the accelerating grid 4 and therefore, if the anode voltage varies, the accelerating grid voltage varies proportionally. It will be seen by reference to Figures 6 and 9 that without the resistance R the change of anode current with anode voltagewill be very small, but that a change of the accelerating grid voltage will produce a large change of anode current. It is of course assumed that the tube is work n above the anode breakdown voltage. By suitably adjusting the value of the resistance R in Figure 10 the anode voltage variations which are thus transferred to the accelerating electrode may be made to cause a considerable change in the anode current, resulting in a large reduction in the anode differential resistance. The result will be an anode current characteristic of the form shown in Figure 11. The slope of this is quite large and because the breakdown voltage falls as 12. is reduced the curve is smooth and continuous from zero upwards. This arrangement is capable of a number of variations. For instance in Figure l2'the tube I has its anode 5 connected to the battery H through a load l5 as before. The accelerating electrode is connected to a tapping on the battery H through a choking coil 12. Condenser I3 will transfer alternating potential variations of the anode to the accelerating grid without providing a path for the D. C. Thus the differential resistance of the tube in this circuit will be a function of frequency. Instead, of the condenser titan A. C. network or tuned circuit may be substituted.

Explanatory theory of discoveries and invention The explanation of the phenomena illustrated in Figures 6-12-may be regarded as followsz- To the best of my knowledge the sudden breakdown of the anode circuit resistance from very high values to very low ones has not been previously demonstrated in practice in the manner shown in Figure 6. It maybe shown from-- velocity the only values which the space current can take up from a cathode to an anode will be either zero or a saturated state when all the electrons leaving the cathode reach the anode. This is because the electrons present at low or zero anode voltage will produce a space charge, equivalent to a definite negative potential gradient in the space between the accelerating electrode and anode, and no current will pass unless the initial velocity of the electrons is sufiicient for them to overcome this opposing gradient. The current will therefore be either saturated or zero in value.

In Figure 1 the electrons passing into the space between the accelerating electrode 4 and the anode 5 will be given a velocity dependent on the voltage of the accelerating electrode 6. Therefore all the electrons may be considered as having substantially the same velocity, and the abovementioned negative potential gradient will be formed in the space between the accelerating electrode and the anode. From the considerations above mentioned it would be expected that, at other than small values of d, on raising the anode potential, no anode current would flow until a certain critical point was reached when the resistance of the tube would suddenly break down and the current would reach a saturated value. In practice the effect of varying values of the initial velocity and of difiusion are not entirely negligible and therefore a small anode current would be expected before this breakdown value of anode voltage was reached,

and for the same reason the breakdown would not be as sudden as the former considerations would indicate. As the potential gradient of the anode will decrease inversely with d, the value of the breakdown voltage might be expected to increase with d. Further, if the initial velocity of the electrons was sufficiently high it might be expected to overcome the negative gradient, even though the voltage on the anode was very small, or even negative with respect to that of the accelerating electrode and therefore tending to decelerate the electrons. In other words one would expect the breakdown to occur in the tube illus trated in Figure 1 before the anode potential reached that of the accelerating electrode if d is not too large. These expectations agree with the phenomena actually found in practice and shown in the curves of Figures 6 and 7. Further. as the anode space current from the filament is reduced the negative gradient will become less and the breakdown voltage be corre- Thephenomena illustratedin Figure 7 may be I explained in greater detail as follows: When the distance d is very small (say 1cm.) in the tube shown in Figure 1, the secondary radiation from the anode 5 when Em is between 100 and 300 volts will be sufficient to cause a large drop in the value of the anode current when the anode voltage is below that of the accelerating electrode 5. Hence at this distance the anode break-' down voltage at which the anode current be--' comes saturated does not occur until the anode voltage is greater than the-accelerating voltage.

thisdistancewill be too great. for secondary radiation which is produced to travel backto the accelerating electrode 4.

' If, however,- the anode is placed a little -further. frorn'the accelerating. electrode 4 (say at 3 cmr);

Then the anode cur rent'will rise toa saturated value, and at an.

anode voltage very much less than that of the accelerating electrode. This corresponds to the lowest point of the curve in Figure '7. If the distance d is increased to say 4 or 5 cm. the secondary radiation will still have no eflect on the result, but, in accordance with the considerations already outlined, the breakdown anode voltage of the tube will be comparatively high. This corresponds to the right-hand part of the curve in Figure 7.

The distance d to the anode or the output electrode in the tube has therefore a definite optimum value and this fact is very important for the operation of the tube.

This critical distance depends also upon the amount and nature of the secondary radiation produced. The effects of secondary radiation have'been investigated by various writers (for instance Hull and Williams in the Physical Review vol. 27, pp. 432, 1926, and Farnsworth in the Physical Review vol. 20, pp. 358, 1922; vol. 25, pp. 41, 1925, and vol. 27. DD. 413, 1926) and the amount and nature of it is related to the velocity of the primary electrons and to the material and configuration of the electrodes from which it is produced. I have found that it is not always possible to obtain the critical distance effect if the velocities of impact of the primary electrons are substantially above a certain value at the surfaces of the electrodes in question for a given size of tube. For instance, in Figure 1, if the voltage of the accelerating electrode 4 (and therefore the velocity of the primary electrons) is too high the amount and velocities of the secondary radiation from the anode will be so great that it will travel back to the accelerating electrode 4 and prevent the anode from being given a lower potential than that of the accelerating electrode without losing the saturated condition. In general, accelerating voltages of several hundred volts may be used successfully in tubes of sizes such as that shown in Figure 1 without detriment to the existence of a critical anode distance.

When large voltages must be employed in order to produce a sufiiciently great current and output power in the stream of electrons from the source of electrons in the discharge tube the primary electrons must be retarded by the use of electrodes having a comparatively low potential which are inserted in the length of the stream before it reaches the anode or other electrode.

A considerable variety of combinations of electrodes are available for any given purpose, examples of which are given below.

In accordance with the invention a further accelerating electrode may be placed between the anode and first accelerating electrode. Prefer ably this is placed at such a distance from the first accelerating electrode that at working potentials of both the current is just above the breakdown point; and the anode is placed at the critical distance from the second accelerating electrode. By the use of additional accelerating electrodes in this manner the length of the stream may be increased without increasing the voltage required to produce it.

As a result of my invention, discharge tubes can be provided, other things being equal with a much greater distance between the anode and accelerating electrode having, therefore, the following advantages:

1) Avoidance of negative differential resistance characteristic because the comparatively low velocity electrons forming the bulk of secondary radiation cannot cross the increased length of gap, while the passage of desired primary electrons to the anode is substantially unafiected.

(2) Reduced inter-electrode capacity, thereby tending to render the operation of the apparatus independent of frequency.

(3) The anode potential may be reduced below that of the accelerating electrode to a substantial extent without reaching the anode breakdown voltage below which the anode current ceases to be saturated, thus enabling an increased output of undistorted power to be obtained in conjunction with the other advantages of the use of a stream of comparatively great length in proportion to its cross-section. Experiment has shownthat my invention enables the passage of saturated anode current in the anode circuit to take place at a lower anode voltage than is possible with other known expedients.

(4) The production of defiectable streams particularly useful in frequency multipliers.

The advantages of the present invention set out in items 1 and 3 are because the increased potential gradient or dip will prevent electrons having a low velocity from passing across the space while allowing the passage of the electrons of high velocity; Secondary radiation consists almost entirely of low velocity electrons and will be stopped; whereas, as previously explained, the primary electrons traveling from the accelerating electrode are all of substantially the same velocity and are of a higher velocity than the secondary radiation to which their impact on the anode gives rise. This is illustrated in connection with the tube illustrated in Fig. 1 by the minimum value of the curve in Fig. 7 and is due to the fact that the two electrodes in question may be separated by such a distance that the velocity of the secondary electrons emitted from the anode is hot sufiicient for them to travel back to the preceding electrode. In addition, if the negative dip is sufficiently great, it is able to prevent an appreciable amount of secondary radiation from the accelerating electrode from traveling to the anode in addition to prevent it traveling in the opposite direction. In both cases, however, the passage of the high velocity primary electrons will be unaffected. These results can only be obtained when an anode is spaced from the accelerating electrode at or about the critical distance.

The valve according to Fig. 13 shows only one accelerating electrode G1 separated from the anode 5 by the critical distance d, as in Fig. 1.

Figs. 14-16 show several possibilities for positioning and arranging the electrodes. The accelerating or retarding grid electrodes in the path of the electrons are designated respectively by G1, G2, etc. The distances between these electrodes are d1, d2, etc. It is obvious that the source ll of voltage is not necessarily tapped at the points shown in the figures under all operating conditions. Sometimes it may be desirable to make the voltage difierence across one part of the distance between the cathode and anode equal to zero, and in this case two or more voltages can be made equal to the critical anode distance in Figs. 13, 14 and 15.

Fig. 14 shows a valve similar to that in Fig. 13 but with the difierence that the distance between the anode and the first accelerating electrode G1 is greater, and that an additional accelerating electrode G2 is provided in the path of the stream. The distance 111 may be selected so that the electrode G2 is operated at a voltage just above the breakdown voltage Eb of the spacing d.

That means that the electrode G2 is situated at the greatest possible distance from G1 (at the given voltages of the electrodes) at which the current remains saturated. The distance between G2 and the anode 5 may be the critical anode distance.

As shown, the electrode G2 has a lower voltage than G1 and therefore works as a decelerating electrode.

The valve according to the invention may also possess an electrode which is at or about the cathode potential and is arranged between G1 and G2 in Fig. 14. The negative potential gradient may be generated partially by such an electrode of low potential, and partially by the space charge.

If in Fig. 14 an electrode at or approximately at the potential of the cathode is added between G1 and G2, it will tend to increase the negative potential gradient in neighborhood of the adjacent electrodes. Experiment shows that it hasa further and a favorable effect in increasing the electrostatic screening between the anode and G1. A valve arranged in this way is shown in Fig. 15.

Fig. 16 shows an arrangement similar to that of Fig. 15, but an electrc'id'eQGt which is wholly or approximately at cathode-potential, is located between G: and the anode 5. It assists the production of the negative potential gradient or voltage drop between G2 and the anode 5, which is produced partly by the electrode G4 and partly by the space charge, as described. The subject-matter of the invention is in this way com bined with suppressor electrodes.

It is pointed out that the critical distance effect will not be produced between two electrodes (e. g. G2 and 5) unless the velocity of the electrons entering the space therebetween has a sufficiently high and approximately single value; thus the positioning and mesh of G4 in Fig. 16 must not be such as to produce such a very low velocity by increasing the negative potential gradient to too great a degree.

Record modulator The application of the present invention to a frequency multiplier tube will now be described with reference to Figures 1'7 and 18.

In addition to the filament 2, Figure 19, focussing hood 3, Figure 20, and first accelerating electrode 24, illustrated in the longitudinal view in Figure 21, the tube also contains an additional accelerating electrode It, a record I! and a target anode 5, Figure 24. The record I! is supported from the side of the tube and consists of a metal disc having slots therein. The slots therein are each covered by a mesh 18 in accordance with the present invention. Certain electrostatic means for deflecting the jet are shown by the plates 20, Figure 22, and are interposed between the second accelerating electrode 14 and the record H.

In accordance with the present invention the distance between the two electrodes 24 and I6 is such that the current between them is above the breakdown point and is saturated. The same conditions hold between the second accelerating electrode and the record H. The anode is placed at the critical anode distance previously referred to. The stream of electrons is influenced by said deflecting means 20 and the position of impact with the record I1 caused to travel over the slots. According to its position in respect to the apertures in the record II, more or less of the stream will reach the anode 5. The anode 5 is connected to an output circuit. Due to the fact that the anode is at the critical distance the voltage variations across this load need not 'prevent the tube from working entirely in a saturated ,conditlon despite the load being such as to reduce the anode voltage very much below that of the other accelerating electrodes.

In Figure a typical curve between the anode current of a tube such as that shown in Figures 17 and 18 and the anode voltage is shown. The voltage of the accelerating electrodes is assumed to be very much higher than Eb in this case. Anode current has been measured with the streampassing through one of the apertures in the record 18, Figure 23. A similar graph having a lower maximum value will be produced when part of the stream is cut off by the record.

By secondary radiation or the like referred to in this specification is meant both reflected and emitted secondary electrons.

According to the invention the grid, accelerating or decelerating, electrodes as mentioned heretofore are formed so as to intercept as little of the electron stream as possible. To do this they are in the shape of a mesh or grid. The sizes of the apertures in the electrodes are not made too large and there are preferably more than one aperture. For example, for the satisfactory operation of the tube illustrated in Fig. 1, an electrode of the kind shown in Fig. 4 is necessary. An important part of my invention is in the fact that I have shown that such mesh electrodes may be made to give satisfactory results in the production of streams of electrons which are of the jet type i. e. are of comparatively great length in comparison with their cross sections. Previously it appears to have been thought essential in endeavors to produce such jets to employ electron "guns or the like of, for instance, tubular, and similar formations. They intercept almost all the space current, or only produce a very small space current, and therefore make the anode current too small to be of use.

The characteristics of means employed to transfer potential variations from one part of a stream to another as in Figs. 10 and 12, may also be arranged to change the characteristics of the said variations when transferred (e. g. change the phase, amplitude and/or wave form thereof). The characteristics of the said means may be a function of other factors, e. g. the frequency of the variations. The potential variations when transferred to different parts of the length of stream may have relatively different characteristics. Therefore, by means of the present invention the differential resistance may be given a series of values including vector forms and complex values which may be dependent on variables which are changeable over a very wide range.

The potential variations across a stream or portion thereof may be transferred to sources of potential in other parts of the streamby suitable electrical circuits, e. g., potentiometer devices, reactive networks, inductive coupling, relaying devices, or the like. Or, if an output circuit is used in conjunction with the tube, potentials may be tapped oif thereacross for this purpose. For example, if this coupling'circuit is inductive and the potentials transferred to the unsaturated part of the stream are tapped off therefrom, a phase difference may exist between the original potential changes and those transferred and if potentials of another phase are applied from the load to another electrode also acting on an unsaturated part of the stream, the current phase will depend on the resultant of all three phases, 1. e. the diflerential resistance will possess a phase angle. If the frequency is varied the phase angles will change, hence the phase angle 01. the diflerential resistance will change also.

Electrostatic screening devices, e. g. metal grids, may be interposed between the electrodes in the tube if required.

The term "auxiliary electrode and anode in this specification and the appended claims are intended to refer to any two electrodes having positions respectively at the beginning and end of.

a portion of an electron stream; and not only to the last two electrodes at the end of the electron stream. The term auxiliary electrode includes both accelerating and decelerating electrodes.

The critical distance" referred to in this specification and appended claims may be defined as the distance between the anode and an auxiliary electrode at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode; when the distance is shorter than this value secondary radiation, when produced at the anode, tends to pass to the auxiliary electrode (when the anode potential is less than that of the auxiliary electrode) and to produce a negative resistance characteristic; when the distance is longer than this value then there is a range of anode voltages from zero upwards over which substantially no anode current tends to be produced. and immediately above this range, the anode current rises abruptly to a saturated value.

It is pointed out that though the critical distance is distinguished from shorter distances by its effect in preventing the passage of secondary radiation (which passes at shorter distances), my invention is not limited to the use of electrodes of material which produce secondary electrons copiously. The operation of the invention does not depend upon producing secondary radiation, but in obtaining the desired ratio between voltage and current intensity by the arrangement which renders feasible, for practical use in incandescent tubes and the like, electron streams which are long and small in cross-section.

It is to be understood that various methods of discharge tube control above described are merely by way of illustrating the invention and that the invention is not limited thereto, but is limited only by the scope of the appended claims.

I claim:

1. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween which consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode and causing such stream of primary electrons to traverse a distance between the auxiliary electrode and the anode at least equal to about the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood or the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode.

2. The method according to claim 1 wherein said stream of electrons is caused to traverse 9.

distance between said auxiliary electrode and anode approximating said critical distance.

3. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween which-consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode, causing such stream of primary electrons to traverse a distance between the auxiliary electrode and the anode at least equal to about the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode, and maintaining the anode potential apart from variation due to a load at a value in excess of-said anode break-down voltage.

4. The method according to claim 3 wherein said stream of electrons is caused to traverse a distance between said electrode and anode approximating said critical distance.

5. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and auxiliary electrodes therebetween, 3 which consists inenergizing the cathode to produce a supply of primary electrons, applying positive potential to said anode to direct such electrons in the form of an electron stream to the anode, applying such voltage to one auxiliary 3 electrode as to increase the velocity of the electrons, applying to a second auxiliary electrode nearer the anode a lower voltage than that applied to said first auxiliary electrode and causing such stream of primary electrons to traverse a distance between said second auxiliary electrode and said anode at least'about equal to the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any, secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of said second auxiliary electrode. 5

6. The method according to claim 5 wherein said stream of electrons is caused to traverse a distance between the electrode nearest the anode and the anode approximating said critical distance. i

'7. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and auxiliary electrodes therebetween, which consists in energizing the cathode to produce a supply of primary electrons, applying positive potential to said anode to direct such electrons in the form of an electron stream to the anode, applying such voltage to one auxiliary electrode as to increase the velocity of the electrons, applying to a second auxiliary electrode nearer the anode a lower voltage than that applied to said first auxiliary electrode and causing such stream of primary electrons to traverse a distance between said second auxiliary electrode and said anode at least about equal to 7 the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented 7 from reaching said auxiliary electrode even though the voltage or the anode becomes less than the voltage of said second auxiliary electrode, and maintaining the anode potential apart from variation due to a load at a value in excess of said anode break-down voltage.

8. The method according to claim 7 wherein said stream of electrons is caused to traverse a distance between the electrode nearest the anode and the anode approximating said critical distance.

, 9. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween which consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode and causing such stream of primary electrons to traverse a distance between the auxiliary electrode and the anode at least equal to about the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode, and applying deflecting forces to the electron stream between said auxiliary electrode and anode.

1D. The method according to claim 9 wherein said stream of electrons is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

11. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween which consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode, causing such stream of primary electrons to traverse a distance between the auxiliary electrode and the anode at least equal to about the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated bysaid anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode, maintaining the anode potential at such value as to produce saturated current between said auxiliary electrode and anode while maintaining unsaturated space current in a preceding portion of the electron stream, and transferring potentials from the saturated part of the stream to the unsaturated part thereof so that such potentials substantially control the current in the saturated part of the stream.

12. The method according to claim 11 wherein said stream of electrons is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

13. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween, which consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode causing such stream of primary electrons to traverse a distance between the auxiliary electrode and the anode greater than the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum, and maintaining the intensity or the electron stream substantially at zero for a considerable part of the range of the potential difierence between said cathode and anode up to the potential difierence at which the stream is substantially saturated.

la. The method according to claim 13 wherein the anode potential apart from variations due to a load in the anode circuit is maintained at a value in excess of the anode break-down voltage.

15. The method according to claim 1 wherein the positive potentials applied to said auxiliary electrode and anode are equal apart from variations due to a load.

16. The method according to claim 1 wherein the positive potentials applied to said auxiliary electrode and anode are equal apart from variations due to a load and said stream of electrons is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

17. The method according to claim 1 wherein the stream of electrons is confined to a path of limited cross-sectional area.

18. The method according to claim 1 wherein the stream of electrons is confined to a path of limited cross-sectional area and said stream is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

19. The method of controlling a stream of electrons in a discharge tube having an anode, a cathode and an auxiliary electrode therebetween, and an additional electrode in the neighborhood of the space between said auxiliary electrode and anode which consists in energizing the cathode to produce a supply of primary electrons, applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to the anode causing the electron stream to traverse a distance between the auxiliary electrode and the anode at least equal to about the critical distance at which the anode break-down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode, and applying to said additional electrode a potential of the order of that of the cathode.

20. The method according to claim 19 wherein said stream of electrons is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

21. An electron discharge device comprising an anode, a cathode, and an auxiliary electrode therebetween, means for energizing the cathode to produce primary electrons, and means for applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to said anode, said auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary to produce primary electrons, and means for applying positive potentials to said auxiliary electrode and anode to direct said electrons in the form of an electron stream to said anode, said auxiliary electrode and anode being spaced apart by distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by the said anode are prevented from reaching said auxiliary electrode even though thevoltage of the anode becomes less than the voltage of the auxiliary electrode, said means for applying positive potential to the anode being such as to maintain the anode potential apart from variation due to a load at a value in excess of said break-down 4 voltage.

24. An elctron discharge device according to claim 23 wherein said stream of electrons is caused to traverse a distance between said auxiliary electrode and anode approximating said critical distance.

25. An electron discharge device comprising an anode, a cathode and auxiliary electrodes therebetween, means for energizing the cathode to produce primary electrons, means for applying positive potential to said anode to direct such electrons in the form of an electron stream to the anode, means for applying such voltage to one auxiliary electrode as to increase the velocity oi the electrodes, means for applying to a second auxiliary electrode nearer the anode a lower voltage than that applied to said first auxiliary electrode, said second auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distanceat which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented 'from reaching said second auxiliary electrode even though the voltage of the anode becomes less than the voltage of the second auxiliary electrode.

26. An electron discharge device according to claim 25 in which said second auxiliary electrode and anode are spaced apart approximately said critical distance.

27. An electron discharge device comprising an anode, a cathode and auxiliary electrodes therebetween, means. for energizing the cathode to' produce primary electrons,'means for applying positive potential to said anode to direct such electrons in the form of an electron stream to the anode, means ior applying such voltage to one auxiliary electrode as to increase the velocity of the electrons, means for applying to a second auxiliary electrode nearer the anode a lower voltage than that applied to said first auxiliary electrode, sa d second auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said second auxiliary electrode even though the voltage of the anode becomes less than the voltage of the second auxiliary electrode, said means for applying potential to said anode being such as -to maintain the anode potential apart from variation due to a load at a value in excess of said anode breakdown voltage.

28. An electron discharge device according to claim 27 in which said second auxiliary electrode and anode are spaced apart approximately said critical distance.

29. An electron discharge device comprising an anode, a cathode, and an auxiliary electrode therebetween, means for energizing the cathode to produce primary electrons, means for applying positive potentials to said auxiliary electrode and anode to direct such electrons in the form of an electron stream to said anode, said auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood oi the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage 01 the auxiliary electrode, and means for applying deflecting forces to the electron stream between said auxiliary electrode and anode.

30. An electron discharge device according to claim 29 in which said auxiliary electrode and anode are spaced apart approximately said critical distance.

31. An electron discharge device comprising a cathode and an anode and an auxiliary electrode therebetween, means for energizing the cathode to produce primary electrons, means for applying positive potential to said auxiliary electrode, means for applying positive potential to said anode as to direct said primary electrons in the form of an electron stream to the anode and pro-' duce saturated current between said auxiliaryelectrode and anode while maintaining unsaturated space current'in a preceding portion of the electron stream, and means for transferring potentials from the saturated part of the stream to the unsaturated part thereof so that such potentials substantially control the current in the saturated part of the stream, said auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even, though the voltage of the anode becomes less than the voltage of the auxiliary electrode.

32. An electron discharge device according to claim 31 in which said auxiliary electrode and anode are spaced apart approximately said critical distance. a

33. An electron discharge device comprising a cathode, an anode, and an auxiliary electrode therebetween, means for energizing the cathode to produce primary electrons, means forapplyingpositive potential to said auxiliaryelectrode, meansfor applying such potential to said anode as to direct said primary electrons in the form of an electron stream to the anode while maintaining the intensity of the electron stream substantially at zero vfor a considerable part of the range of the potential difference between said cathode and anode up to the potential difierence at which the stream is substantially saturated, said auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode.

34. An electronv discharge device according to claim 33 in which the anode potential apart from variations due to a load in the anode circuit is maintained at a value in excess of the anode breakdown voltage.

35. An electron discharge device according to claim 21 in which the positive potentials applied to said auxiliary electrode and anode are equal apart from variation due to a load.

36. An electron discharge device according to claim 21 in which the positive potential applied to said auxiliary electrode and anode are equal apart from variation due to a load and said auxiliary electrode and anode are spaced apart at approximately said critical distance.

3'7. An electron discharge device according to claim 21 in which means are provided for confining said stream of electrons to a path of limited cross-sectional area.

38. An electron discharge device according to claim 21 in which means are provided for confining said stream of electrons to a path of limited cross-sectional area, and said anode is spaced from'said auxiliary electrode by a distance approximately said critical distance.

39. An electron discharge device comprising a cathode, an anode, and an auxiliary electrode therebetween, an additional electrode in the 5 neighborhood of the space between said auxiliary electrode and anode, means for energizing said cathode to produce primary electrons, means for applying positive potentials to said auxiliary electrode and anode to direct such electrons in the 10 form of an electron stream to the anode, said auxiliary electrode and anode being spaced apart by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially l5 saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the voltage of the auxiliary 20 electrode, and means for applying to said additional electrode a potential of the order of that of the cathode.

40. An electron discharge device according to claim 39 in which said auxiliary electrode is 25 spaced from said anode at approximately said critical distance.

41. An electron discharge device according to claim 21 in which said auxiliary electrode has' apertures therein of such dimensions compared 30 with the distance between the auxiliary electrode and the cathode that the electrostatic field produced by said auxiliary electrode is substantially uniform in the space betw'eenit and the cathode.

JOHN HENRY OWEN HARRIES. 

